Many different electrical wiring devices installed into the electrical circuits of premises, including residences, offices, businesses, factories, public buildings and other buildings require DC power whenever control circuits are used for the electrical wiring devices, including circuits used for measuring and communicating power consumption.
Electrical wiring devices for controlling LED lights, home automation switches and relays, controlled power outlets and environment control devices such as controls for heating, cooling, motorized window shades and curtains, installed into electrical wall boxes cannot be powered by a separate low voltage DC power lines, nor via a low voltage communication line. The electrical and building codes strictly prohibit the connections of low voltage bus-lines and/or the mingling low voltage wires with wall mounted AC power devices and/or with AC power lines in the same conduits. It would be similarly against the electrical and safety rules to connect low voltage communication wires to a current sensing adaptor, such as a plug-in adaptor for use with AC outlets of the present invention. Low voltage bus-lines cannot be directly connected to AC wiring devices for reporting to a controller the power consumed by an appliance.
This mandates the use of AC power supplies, internally built into electrical outlets, switches, relays, dimmers and the like. Such power supply may use AC transformers or large AC capacitors that are bulky and costly. Alternatively such small power supply may use power switching circuits that are costly and generate noise that must be suppressed by bulky filters.
Analog methods and devices to convert AC power to a low voltage and low current DC power are simple and generate very little noise, yet analog regulators waste substantial power and the resulting heat must be dissipated. The wasted energy by the analog regulator is far above the actual energy needed to power a control circuit of a given device to operate, particularly when the control circuits consumes very low power of few mW, or DC current of few mA and a low DC volt such as 5V, 3.3V or 1.8V for its operation.
Such low power consuming control circuits including controls for dimmers, current sensors, relays, power outlets and similar devices, using low power consuming CPU are disclosed in U.S. Pat. Nos. 7,639,907, 7,649,727, 7,864,500, 8,041,221, US publications 2010/0278537, 2011/0227510, 2011/0311219 and U.S. patent application Ser. Nos. 12/963,876 and 13/086,610 are incorporated herein by reference and are referred to hereafter as the reference patents, publications and applications.
The power wasted by the power supplies of AC power outlets or of a plugged-in power sensing adaptors incorporating power consumption detecting and communicating circuits are significant for the attempts by the global community to reduce the power consumption by monitoring the power consumed through power outlets in residences, commercial and industry use.
The current and power drain measuring and reporting circuit may drain few mW (milli Watt), but even if the power supply is efficient, the conversion of 120V or 230V AC into 1.8V/1 mA DC power will consume 1 W or more from the AC power line. Such continuous drain of power by, for example thirty power outlets and ten switches of a small residence, will waste energy of 40 W/hour or about 1 KW/day. This will occur even when not a single appliance or light is operated or even connected to the AC outlets. The accumulated wasted energy will therefore be over 365 KW/year by a small typical residence, such as a two small bedroom apartment. This is a significant consumption that must be resolved. A new small size low cost AC to DC power supply that does not waste energy is needed.
Common AC current sensors and current measuring elements include AC current transforms and coils for detecting current by induction, very low ohmic resistors such as 2 mOhm or 10 mOhm, for detecting the current passing through them by the level of voltage developing over the resistors terminals and magnetic hall sensors for detecting the magnetic flux by a current drain in a conductor.
The induction sensing element, the low ohm resistor element and the hall sensors present structural and assembling method difficulties that are not simple to solve. This directly affect the needed simplified low cost current sensing solution for reporting current consumption by appliances and other loads, and the accuracy of the very wide ranging unpredictable and randomly consumed power.
The low ohmic resistors used for AC current measurement are typical structured resistors, similar to the well known axial resistors or surface mounted resistors for mounting onto printed circuit board patterns. The axial resistors can be soldered onto terminals and other metal structure by a procedure that may affect the value of such small value resistances ranging for example from 2 mOhm˜20 mOhm.
Further the low ohmic resistors need to be introduced for measuring higher currents ranging for example, from 5 A to 20 A or even higher, mandating PCB patterns that are wide end thick, or terminals that are large sufficiently to carry such heavy current without generating heat.
On the other hand the current transformers for detecting the AC current by induction are made of larger coils and/or cores, for measuring low current such as few mA to increase the permeability and the magnetic flux for measuring few mA of current drain. This is to enable the current transformers to output signals that are measurable and/or can be differentiated from noise levels that are persistent in power lines and the AC wiring devices of the electrical system.
Therefore the use of prior methods, elements and components results in large and bulky units, difficult to introduce into small current sensor adaptors or into AC outlets and switches mounted into electrical wall boxes. The same applies to plug-in current sensors, they must be made to be esthetically and small in size to be pleasing and not large bulky obstructive device plugged-in the AC wall socket and onto decorative covers of such AC outlets.
The hall sensors used for AC current sensing are small and accurate but require some 40˜100 mW (5-10V and 8-10 mA) to operate, which contradict the need to minimize the wasted power by the current sensing circuit itself, the power supply and the wasted power by the AC current detecting devices. Here too another solution is needed.